There's a scene in the movie Missing where Captain Ray Tower, the US Naval Intelligence officer, gives Beth, the Leftist hero's girlfriend, a piece of advice.

"You gotta learn to stay ahead of the power curve, kid. You know what I mean? It's an old aircraft carrier term. If a pilot gets ahead of the power curve and something happens, then he can pull up and away. But if he falls behind the power curve and something happens, then it's adios. You gotta stay ahead of the power curve, kid."

By now David Cunliffe will have a pretty good idea of whether he is ahead of, or behind, the power curve that is about to determine the Labour leadership. My guess is, he is behind. My guess is David Shearer will have enough support to win the caucus vote on Tuesday.

If Mr Cunliffe remains on his present course, then, in the words of Captain Tower, "it's adios" to his leadership hopes. He will have fallen behind the power curve.

But, there's still a way Mr Cunliffe's fighter plane can clear the aircraft carrier's deck. Because, from the moment David Parker abandoned the race and released his supporters, Mr Shearer has also been behind the power curve. If Mr Shearer wants to get ahead of the power curve, then he is going to need Mr Cunliffe.

How can this be? How can Mr Shearer be poised to become Labour's leader and yet lack the power to get his plane off the flight deck? The answer lies in the composition of Mr Shearer's support.

When he, almost casually, added his name to the list of leadership candidates on November 29, I really don't think Mr Shearer had much of a game plan beyond signalling to his colleagues that, at some point, but probably not this point, he might be considered for the top job. What he failed to grasp was that by adding his own candidacy to the leadership contest he had unwittingly strengthened the hand of Mr Cunliffe's enemies.

Before Mr Shearer's announcement, the "Anyone But Cunliffe" (ABC) clique had been forced to place all its hopes on Mr Parker. But, as the three-Davids encounter on TVNZ's Close Up cruelly exposed, Mr Parker was never going to beat Mr Cunliffe. Mr Shearer, on the other hand, had looked like a winner.

Almost overnight, Mr Parker found himself abandoned by his erstwhile backers. Even Grant Robertson, the man Mr Parker had nominated as his preferred deputy, snuck off to "Camp Shearer". Stricken, Mr Parker withdrew from the race and threw his support behind Mr Shearer.

Now Mr Shearer was a serious contender, but his new front-runner status came at a price. Like David Lange before him, he was no longer his own man. Labour's spent forces, the MPs epitomised by the politically exhausted figure of Trevor Mallard, were now wrapped around Mr Shearer like supplejack around a totara. And they were clinging to him for only one reason: survival. Their arch-enemy, Mr Cunliffe, had long ago read their use-by dates. That's why the ABCs couldn't allow him to win.

If Mr Cunliffe cannot beat Mr Shearer, then he should, over the next 72 hours, think very seriously about joining him. It's not too late for the best qualified candidate to contact the most popular candidate; set up a meeting; and make a deal. Mr Key and Mr English did it - why not Mr Shearer and Mr Cunliffe?

Together, they've more than enough strength to tear off and make a bonfire of all that parasitic caucus supplejack. Together, they could bend the arc of history towards a Labour victory. Together, a new power curve could hurl their fighters skywards heading for the National fleet.